LED backlight not turning on

I was given a Late 2010 11" Macbook Air (A1370) by a friend. He spilled a small amount of tap water on the keyboard (he thinks it only hit the keyboard). After that the thing was dead. It wouldn't power up no matter what you did or incantations were were attempted.

Eventually I opened it up. I figured I had nothing to lose as it was out of warranty and he had already replaced it with a newer 13" model. I have plenty of experience working on electronics. I've fixed phones, laptops, desktops, home wiring, and industrial equipment.

I did notice some mineral staining on the logic board from where the tap water had dried. I carefully washed the board with lint free wipes and isopropyl alcohol. After a few tries and a bit more cleaning especially on the narrow pitch connector that runs to the display, I managed to get the thing to boot.

It booted as expected, chime, and eventually the login screen. The only problem is that the LEDs for the backlight refuse to turn on. The only way I can tell that they system is booted is by holding up the entire laptop to a light so that the center of the screen where the Apple logo is located is lit. I can see the login screen with his name just as one would expect. I don't doubt that if I were to connect an external monitor that it would work fine (the only reason I haven't done this is I don't feel like buying the adapter as that's not how I want to use the computer).

If this were a CCFL backlight display I'd just assume that the inverter for driving the high voltage lamps was fried. The thing is, this being an Air I don't believe there is such an inverter (most LEDs operate below 12 volts so there's no need for such a device.

Is there by chance a fuse or other such device that I might have missed on the logic board? Are there any test points to see if the requisite voltage is being delivered at least as far as the display connector? I have the equipment necessary to test including a nice multimeter from Fluke and an oscilloscope, although I can't imagine needing the later.

If power is indeed being supplied to the connector (I wish I had the pinout) It would seem that my next step is an unenviable one of removing the bezel that surrounds the screen and is glued on. I have an adjustable temperature heat gun and don't doubt that I can remove the bezel.

Once the bezel has been removed along with the polarizer and diffuser sheets I'll have access to the LCD and the LED backlight assembly.

What I need to know is if the LED assembly has any real circuitry on it aside from the LEDs themselves. The few pictures that I've seen of the backlight assembly appear to show only LEDs on a sheet of flex circuit with an edge connector. That would lead me to believe that the assembly is entirely passive and there's not much to go wrong with it.

So... what would be my suggested course of action? If there are any fuses I'd love to test them, I just need to know where they are located. While I'd like to avoid removing the display bezel and disassembling the upper structure I'll do it if there's a chance that the problem is indeed contained within its glued chassis.

Thank you for any tips, data sheets, repair guides, or anything else, especially your time.

--adam

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adam, it would help if you can post a high-res image of your logic board with the question. Also, please verify the number of your logic board. It should be something like 820-xxxx

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Adam Hunt, your logicboard does have a backlight fuse. It is reference designator F9700 and is a 3AMP-32V-467 in a 603-HF package. See if the schematic for the connector will help you out. The LCD is totally passive. Everything happens on the logic board. You also want to check the Mosfets Q9706 and Q9707 around the fuse. Hope this helps, good luck.

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It could be How to tell if MacBook Pro LED fuse is bad or screen... either are an advanced DIY repair... the easier fix, replace the entire logic board.

Some good advice/experience about this problem/repair.

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